This invention relates to distributed modem pooling techniques for maximizing resource utilization in an xDSL communication network, and more particularly, for maximizing resource utilization of the network when call sessions are idle.
Modem concentration facilities, such as a telephone company""s Central Office (CO), serve as communication links between subscriber lines and a digital network such as the Public Switched Telephone Network (PSTN). Modems provide part of the interface between subscriber lines and a digital network such as the PSTN. In its simplest form, a modem is a device that adapts a digital signal to a telephone line. It converts a desktop computer""s digital data, for example, into audio-frequency analog signals to be transmitted over a telephone channel, and then back to digital form at the opposite receiving end. Modems also include functionality to dial the line, answer a call, and control transmission speed. During data exchange along a subscriber link, new modems have built-in error correction, automatic feature negotiation, and other similar techniques to ensure proper transmission and reception of data.
Increased communication of digital data across subscriber links has led to a proportionate investment by phone companies into new and existing infrastructures to meet the bandwidth requirements needed to handle the additional traffic. One area in which enormous investment has been required is in linking Internet Service Providers (ISPs) with their clients (Internet users) across the PSTN backbone. The required investment in this area has been increased as a result of industry practices that partially relieve the ISPs from the full cost of PSTN connections. Because the ISPs do not therefore pass the full cost of these connection times on to their clients, i.e., they bill them at flat rates, the clients engage in practices that waste the limited resources of the network. One of these practices involves a client establishing a connection with an ISP and maintaining it indefinitely even during long periods of inactivity, consequently, tying up a network resource unnecessarily. Such long idle periods of time are common place in today""s data communication networks. Also, another type of idle exists as a result of the bursty nature of Internet traffic in which shorter idle periods of time are sandwiched between successive transmission bursts.
Because most Internet users communicate with their host ISPs over analog subscriber lines across a digital circuit-switched network, such as the PSTN, the congestion problem is most severe in those networks. The least cost-effective and most inefficient way of adding resources to handle this congestion is to increase the number of modems (in the form of modem pools) available for call sessions. When active data traffic becomes low, a significant number of these modems in the pool will remain mostly idle and underutilized resulting in a waste of network resources.
One approach to overcoming this problem is to detect the link""s idle state and, consequently, terminate the call and make its resources available to other network users. However, reestablishing the communication link when the user desires to reactivate the call session is a complicated process which results in a lengthy delay and could prove to be impossible if all resources are presently tied up in the network. Generally, establishing an xDSL modem link over a digital circuit-switched channel is very time consuming. For example, connecting an ADSL call at the physical layer may take 15 to 20 seconds. Incurring such a delay for every data communication restart is clearly impractical.
The inventors have determined that what is needed are ways to better manage network resources such that processing capabilities of modems associated with idle call sessions are better utilized without disruption of their underlying physical layer link. The present invention provides efficient alternative solutions.
The invention provides a system and method for managing resources in a distributed xDSL modem pool arrangement including a first number of front-end modules and a second number of back-end modules. In the preferred embodiment, when a back-end module identifies that its associated call session has entered idle-mode, idle-mode processing is performed in a manner which reduces processing load and electrical power consumption but does not result in a loss of synchronization or require retraining.
The invention relies on the generation of a repetitively transmitted single modulated symbol generated by an end user device during idle periods in user data. In the preferred embodiment, the modulated symbol to be transmitted is selected such that its spectral properties match those of user data modulated symbols. For an ADSL system, and the like xDSL variants thereof, a preferred idle symbol is the xe2x80x98superframexe2x80x99 synchronization symbol. A separate modulated symbol would indicate the end of the idle state. In accordance with the present invention, the processing of idle symbols is entirely (or substantially) handled by the front-end module thus freeing up the associated back-end module which may be reassigned to another call session at that point; or to the extent the front-end to back-end link is maintained, the back-end processing demands are reduced which may allow the back-end module to provide service to another call session. In the case where the back-end is reassigned, full control of idle symbol processing may be handled by the low-cost front-end module. When active data appears on the subscriber link, the xDSL call session link may again be established bringing any of the available high-capability back-end modules on line.
In accordance with a preferred embodiment, the front-end modules are physically separate low cost devices provided with only such processing power, including memory and programmed functionality, necessary to perform reduced complexity time-domain processing in idle-mode where each front-end module requires negligible processing resources to detect and process idle symbols being transmitted from the user device. Very little power is required by the front end module during idle-mode thus resulting in improved power consumption being realized without tearing down the call session physical layer link. As for the associated back-end module, this modem resource may be powered down altogether or reassigned to a new non-idle call session.
In another preferred embodiment, the front-end modules are provided with sufficient processing power, including memory and programmed functionality, to maintain more than one subscriber link active, at least during idle processing of such links.
In yet another embodiment, the front-end modules and back-end modules are each fully functional xDSL modem devices capable of operating as either front-end devices or back-end devices, respectively, on an as needed basis.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.